PROJECT SUMMARY Fatal overdose from opioid misuse is one of the most pressing issues affecting the modern world. As one of the nation?s leading preventable causes of death, a critical line of defense against opioid use disorder (OUD) must be standardized screening provided by the patient?s primary care physician, psychiatrist, and/or counselor. Standardized screening methods for opioids, however, are simply inferior and no gold standards exist. Reform proposals call for improved technology for electronic screening to save time and improve standards of care. Moreover, the National Institute of Mental Health?s Research Domain Criteria (RDoC) framework prescribes a focus on defining the underlying functional dynamics of OUD instead of using symptom-based tools as biomarkers for disease. Therefore, the present proposal aims to develop a validated, theoretically-guided tool, which provides clinicians with information beyond OUD symptoms. Reinforcer pathology is a measure of severity derived from the synergy between two distinct decision-making processes, 1) preference for immediately available small rewards (i.e., excessive delay discounting) and 2) over-valuation of substances such as opioid prescription pills (i.e., high behavioral economic demand). Paramount to this proposal, decades of research have concluded that delay discounting and demand are highly correlated with substance use severity and important predictors of OUD treatment success. In order to develop a feasible and acceptable reinforcer pathology-based mobile tablet application, BEST-OUD, for use in the clinic, the present proposal aims to recruit clinicians to provide feedback via semi-structured interview sessions (Aim 1), and integrate the BEST-OUD application into their practice (Aim 3a). Development, iteration, and maintenance of the app, including the user-interface and back end, secure database, score calculation, and associated web portal will be built and maintained by BEAM Diagnostics, Inc. (Aim 2). A total of three tool prototype iterations, based on clinician feedback, will be administered to clinic patients throughout the testing period to collect reinforcer pathology scores and patient feedback (Aim 3b). This reinforcement pathology assessment tool is innovative given its propensity to bypass self-report of past substance use behavior and OUD symptoms, and prospectively predict severity based on a theoretical framework, making this Phase I STTR application both timely and necessary.